Reduction Process Of Graphene Oxide Research Articles

Tuning the oxygen functional groups in graphene oxide nanosheets by optimizing the oxidation time

The most widely used method for the synthesis of graphene in large scale is through the thermal exfoliation and reduction process of graphene oxide (GO). Well know that the physicochemical properties of graphene greatly affected by the oxidation time employed in GO preparation. In this study, GO samples were prepared at different oxidation time through the Hummers' method. The formation of oxygen containing functional groups in GO and their influences onto its’ structure were analyzed and compared. XPS analysis and 13 C NMR revealed the formation of carboxyl groups mainly formed at a longer oxidation time. XRD results obtained indicated that the oxidation time have no effect on the interlayer spacing ( d ) once it reached the optimal extent, however, the graphite stacking order was disrupted due to the insertion of oxygen-containing functional groups. The influence of oxidation time on the stability of GO dispersions was evaluated by zeta potential , which exhibited higher zeta potential and stability at longer oxidation time. This study demonstrates that the integrity and physicochemical properties of GO can be tuned and depend on the type of oxygen-containing functional groups generated at the basal or edge structure, which may foster a range of new applications. • High integrity of GO structure with enriched oxygen functional groups is accomplished within 5-days of oxidation time. • Epoxide and hydroxyl species abundantly formed within 5-days of oxidation time. • Oxidation time is no longer affected the d-spacing of graphitic structure once it reached to the optimal extent. • The oxidation process mainly occurred at the periphery after 5-days oxidation time. • High stability in colloidal system is accomplished in GO with 5 and 7-days oxidation time.

Synthesis of graphene oxide and its reduction by green reducing agent

A low cost and environment friendly green reducing agent ascorbic acid also known as vitamin C is used for reduction process of Graphene Oxide. Graphene Oxide was synthesized by Modified Hummer’s method where NaNO 3 is removed by increasing the amount of KMnO 4 . The degree of reduction is controlled by varying the amount of ascorbic acid without losing properties of reduced graphene oxide. Surface and structural properties were studied by X-Ray Diffraction, UV– visible, FTIR and RAMAN spectroscopy. FTIR confirmed that most of the groups like hydroxyl (–OH), epoxy (C-O-C), carboxyl (–COOH) and carbonyl (C = O) are removed during reduction process. Vitamin C is easily available and is found to be better replacement for reducing agents like hydrazine and sodium borohydride which are potentially toxic. Graphene and its derivatives are the basic materials used for a number of applications in composites, sensors, nanoelectronics, etc.

Using nitroaromatic fused-heterocycle molecules as nitrogen source to hugely boost the capacitance performance of graphene

Nitroaromatic pollutants with unusually strong adsorption affinity are highly attractive candidates for creating 2D molecular assemblies on the surface of graphene, which is crucial to prepare high-quality N-doped graphene by post-treatment. Herein, the few-layered crumpled N-doped graphene (5-NIGN) with high N content is successfully prepared by mixing 5-nitroindole (5-NI), ammonia, and graphene oxide (GO) and using a simple hydrothermal method followed by the post-treatment process of vacuum freeze-drying and annealing. It is found that the rapid assembly of 5-NI effectively suppresses the aggregation of the products in the reduction process of GO, so that the thickness of as-prepared 5-NIGN is 4.21 nm, very close to that of GO (4.01 nm). Compared with the N-doped graphene (GN) derived from the system of GO containing ammonia (341 F g−1), 5-NIGN exhibits higher capacitance of 457.4 F g−1 at 1 A g−1 and prominent long-term life (115% of capacitance maintenance upon 10,000 cycles) within the voltage window of 1.0 V. Furthermore, the supercapacitor assembled by 5-NIGN electrodes can deliver the energy density of 15.5 Wh kg−1~18.5 Wh kg−1 at the power density of 8000 W kg−1~800 W kg−1. These results indicate that the 5-NIGN material will have potential advantages in the realm of electrochemical energy storage.

Well controlled reduction, N-doping and cross-linking of graphene hydrogel: As good template for photocatalytic reaction

The combination of semiconductor nanoparticles (NPs) and graphene in the form of composite aerogels has become a valid strategy for improving the photocatalytic performance. However, the disorderly aggregation of NPs and the complexity of the synthesis process remain as great challenges limiting the applications. Herein, we put forward a graphene hydrogel template for convenient and accurate synthesis of three-dimensional ZnO/nitrogen-doped (N-doped) graphene aerogel by well regulating the reduction process of graphene oxide (GO) flakes based on thermodynamic analysis. The control-formed hydrogel template with moderate reduction degree retains adsorption sites for Zn2+, assuring the formation of well-distributed ZnO NPs on the three-dimensional N-doped graphene network. Owing to the synergistic effect between ZnO NPs and graphene network, the composite shows excellent photocatalytic performance under visible light. Besides, by pre-introducing common polymer fibers into the preparation system, big size composite aerogel could be easily produced, which ensures the facility for the large-scale practical applications.

Performance of graphene-based hydrogel in oil removal using graphene oxide derived from powder and flake graphite

Graphene-based hydrogel had been formed by chemical reduction process of graphene oxide using ascorbic acid as a reducing agent in this study. Oil adsorption capacity of the hydrogels that were synthesized using different parameters, including type of graphene oxide feedstocks (powder or flake graphite), concentration of graphene oxide used (2 mg/mL or 5 mg/mL), as well as the amount of ascorbic acid added into the graphene oxide (5 grams or 8 grams), had been evaluated in this work. Fourier Transform Infrared Spectroscopy (FTIR) results showed that the oxygen-containing functional groups which were initially present in the graphene oxide could be removed or reduced to form the 3-dimensional π-π interactions hydrogel. In overall, hydrogel produced from flake graphene oxide with the use of higher concentration of graphene oxide (5 mg/mL) and the lower amount of ascorbic acid (5 g), showed the best performance in oil adsorption capacity. The hydrogel produced from these parameters showed the highest adsorption capacity of 7.90 g of oil adsorb per g of hydrogel. This study has provided useful information on the functional groups of graphene-based hydrogels in addition to their oil adsorption capability.

Low cost and green approach in the reduction of graphene oxide (GO) using palm oil leaves extract for potential in industrial applications

Graphene is an exceptional and versatile new material which having worldwide reputation due to its unique properties such as having extremely good electrical conductor, tunable energy band gap, and offers high mechanical strength. The process to derived graphitized carbon into the reduced graphene oxide (rGO) is facing a huge obstacle and the chemical method is proven to be the best choice in order to synthesis rGO in the big scale short amount of time. However, the current chemical method involved the usage of hazardous, toxic and corrosive chemical as reducing agent namely hydrazine to form the sheet layer of graphene. Thus, this will limit the various applications of graphene due to environmental impact and safety issues. As an alternative current research proposed the usage of palm oil leaves extract to replace the hazardous and toxic chemical used as reducing agent. In our project, graphite was used as starting material and was oxidized using modified Hummer’s method. The palm oil leaves extract with the mixture of graphene oxide (GO) solution was refluxed to produce rGO. The as-synthesized green approach rGO material were then characterized using X-ray diffraction (XRD), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), and Raman spectroscopy. The results revealed that the interspace distance between plane increased proportionally as graphite was oxidized, increasing from 0.33 nm to 0.84 nm. The reduction process of GO using palm oil leave extract showed the successful in removing the hydroxyl group and amorphization of sp2 carbon structures. The reduction process found to be increased in C/O ratios from 1:1 to 3:1. Raman spectroscopy revealed that the G band position was restored comparable to graphite as the reduction process successful achieved. TEM images and selected area electron diffraction (SAED) patterns illustrated the confirmation of the successfully synthesized of the monolayer of graphene sheet. Electrochemical studies carried out for both GO and rGO have positively differentiated and concluded a better voltage-current response of rGO in comparison to GO. The as synthesized rGO in the current project holds various potential for further investigation and industrial applications not limited to just supercapacitor and photocatalyst.

Comparative gas sensing analysis of green and chemically reduced graphene oxide

The current study reports the comparison of green (L-Ascorbic acid) and chemically (hydrazine hydrate) reduced graphene oxide (RGO) for NO2 chemiresistive gas sensor. The reduction process of graphene oxide (GO) involves removing oxygen-containing functional groups to form a highly reduced RGO having a large surface area and high adsorption capacity, which makes it very efficient for gas sensing applications. Very few comparison studies were carried out on gas sensing performance based on an eco-friendly non-toxic green approach and chemically effective method used for GO reduction. RGO reduced with hydrazine hydrate (RGOH) has exhibited better sensitivity (80%), the low response time (4s), and recovery time (7s) as contemplated to green reductant L-AA (RGOA). However, based on economic viability and environmentally safe preparation method, RGOA can be utilized for gas sensing application in place of RGOH, despite 10% lower gas sensing performance compared with RGOH.

Enhancement of Voltammetric Signals Using a Graphene Oxide Modified Carbon Electrode for Electrochemical Paper-Based Analytical Devices

This work presents an enhancement of the voltammetric signal on an electrochemical paper-based analytical device (ePAD) using a graphene oxide (GO) modified carbon electrode. The ePAD is fabricated using a screen printing technique for fabrication of the hydrophobic area and three electrode strips. The graphene film was directly prepared on ePAD by dropping 2 µL of GO dispersed in water onto the working electrode surface and leaving it to dry at room temperature. The electrochemical reduction process of GO was carried out by applying a constant voltage of -1.20 V (vs. Ag/AgCl electrode strip) in 0.1 M KCl for 800 s. The GO-modified carbon working electrode on ePAD was readily obtained and ready to use after removing KCl solution. We tested the enhancement of the voltammetric signal on ePAD with a 6 mM [Fe(CN)6]4–/3– redox couple in 0.1 M KCl supporting electrolyte solution. Our results obtained from cyclic voltammograms showed that the unmodified working electrode and the GO-modified working electrode on ePAD provided similar anodic and cathodic peaks. Due to accelerated electron transfer process, it was found that the GO-modified working electrode on ePAD provided approximately a 2-fold increase in voltammetric signals when compared to the unmodified working electrode on ePAD. The reproducibility (inter-day precision) of the voltammetric signal measurement using a GO-modified working electrode on ePAD was acceptable. The relative standard deviation (RSD) was 5-8%. Therefore, the GO-modified carbon working electrode on ePAD offers an effective approach to enhance the signal and sensitivity for chemical analysis.

Conductivity Modification of Reduced Graphene Oxide (rGO)

In the traditional circuit board metallization process, the electroless plating process is the most common, but it contains precious metals (such as palladium catalyst), formaldehyde and chelating agents which can cause a serious environmental problem. However, the direct reduction process of graphene oxide (GO) does not include the toxic as mentioned above. In additionally, reduced GO (rGO) can be regarded as a direct plating process (i.e., without electroless deposition before copper electroplating) is simpler than electroless plating process and can replace the electroless plating process to achieve a green metallization process. Although rGO is a good electric conductor, copper is difficult directionally deposited on it due to its p-electron characteristics, which transfers only in X-Y two-dimensions. Therefore, when rGO is electroplated in a copper electroplating solution, the deposited copper crawls initially from the cathodic terminal and then fully cover the rGO-coated substrate if the surface area of the substrate is large. In this work, we propose an approach to enhance the conductivity of rGO in Z-direction, so that rGO will have three-dimensional conductivity to meet the industrial requirement.

Surface functionalization of graphene oxide by disodium guanosine 5′-monophosphate and its excellent performance for lipase immobilization

Abstract In order to solve the toxic and hazardous issues of the agents in the chemical reduction process of graphene oxide (GO), disodium guanosine 5′-monophosphate (GMP-2Na) was used as an ideal reducing agent for the synthesis of functionalized GO (FGO) for lipase immobilization. At the condition of low amount adsorption of GMP-2Na indicated by the N1s spectra of X-ray photoelectron spectroscopy (XPS), the C/O atomic ratio of the FGO increased from 2.09 to 3.12, indicating the reduction of GO. As the amount of GMP-2Na increased, the intensity of the characteristic peak of GO in the XRD pattern decreased, and the I D /I G peak intensity of Raman spectra increased during the functionalization process. It was found that when the concentration of GMP-2Na is 0.20 mg/mL, the degree of hydrophobicity of FGO is conducive to the formation of optimal conformation of lipase. After immobilization, the activity of the immobilized enzyme reaches twice the value of free enzyme. At the same time, the protein loading reaches to 600 mg/g. The immobilized enzyme showed enhanced durability since no obvious decrease was observed after incubation for 8 h at pH 6.0 and pH 7.0. After storage for 35 days, the activity of GO-G@ enzyme was 54.47% higher than that of free enzyme. GO reduced by GMP-2Na provides a possibility to obtain a highly efficient lipase immobilization carrier.

The experimental and theoretical insights towards the CO induced Pd-Graphene and their multifunctional energy conversion applications

Here, CO gas environment has been used for reduction of graphene oxide (GO) and Pd precursor for preparation of varieties of Pd Nanostructures (PdNSs) with different shapes, size and surface morphologies on graphene support (RG-PdNSs). The extensive ab-initio Molecular Dynamics (MD) simulations and electronic structure calculations have been carried to get theoretical insight for the reduction process of GO by CO. The reduction of GO by CO as observed in experiment are confirmed by ab-initio MD snapshots at different time steps, energetic of the process and the Partial Density of States character of O2p orbital of GO before and after interaction with CO. The discrete states in the Partial Density of States of O2p orbital after CO attack indicates detachment of O from GO. The as-prepared RG-PdNSs are thoroughly characterized by different techniques. The simulation reveals the change in electronic properties from semi-metallic in pristine graphene to metallic due to the attachment of Pd in RG-PdNSs. The electrocatalytic activity of the as-synthesized nanostructures has been investigated toward the multi-functional energy conversion applications, the methanol oxidation reaction, formic acid oxidation reaction and oxygen reduction reaction. The RG-PdNSs exhibit excellent electrocatalytic performance compared to that of unsupported PdNSs and commercial Pd/C.

The fabrication of graphene-polypyrrole composite for application with dye-sensitized solar cells

Abstract This research is to study the preparation of graphene-monodispersed polypyrrole composite materials for uses as a counter electrode in dye-sensitized solar cells (DSSCs). The preparation started with the synthesis of graphene oxide (GO), followed by the preparation of composite films by polymerization method and the GO reduction process by ascorbic acid. The characterizations included thermal-gravimetric analysis (TGA), fourier transform infrared spectroscopy (FTIR), raman spectroscopy, X-ray diffraction (XRD), field-emission electron microscopy (FESEM) and cyclic voltammetry (CV). The DSSCs’ efficiency tests were also conducted and analyzed. Based on the test results, it was found that DSSCs prepared from PPy/RGO-5 composite films with 5% by weight of reduced graphene oxide (RGO) could give an optimal efficiency. Nevertheless, the efficiency of such solar cells was much less than that of DSSCs with platinum counter electrode. This could be due to incomplete reduction of graphene oxide, resulting low electron transfer ability and electrocatalytic activity toward the reduction of electrolyte solution.

Stabilization of aqueous graphene oxide with acetone under γ-ray/UV irradiation

Graphene oxide (GO) is a kind of water soluble two-dimensional materials containing a large amount of oxygen-containing groups which infuse GO with water solubility, biocompatibility and functionality, etc. But GO can be easily reduced by losing oxygen-containing groups under some circumstances such as irradiation of $\gamma$ -ray or ultraviolet (UV). In this work, we found that acetone can significantly slow down the reduction process of GO under the irradiation of either $\gamma$ -ray or UV, which was supported by analysis results with UV-visible (UV-Vis) absorption spectra, X-ray photoelectron spectroscopy, etc. Acetone can capture and remove strongly reducible hydrated electrons generated under $\gamma$ -irradiation. GO reduction by UV also involves electron transfer process which can be affected by the presence of acetone. Hence, acetone can be used to stabilize, adjust the radiation reduction process of GO. This would be interesting not only in radiation and radiation protection, but also in understanding the redox properties of GO.

Preparation of TiO<sub>2</sub>-Reduced Graphene Oxide Nanocomposites for Sunlight Degradation of Methylene Blue

Photogenerated electron/hole recombination greatly limits the catalytic efficiency of TiO2, and recently modification with graphene substance has been regarded as an effective way to enhance the photocatalytic performance of TiO2. When referring to the fabrication of graphene based materials, the reduction process of graphene oxide has been demonstrated to be a key step. Therefore, it is highly required to develop an efficient and simple route for the GO reduction and the formation of TiO2-reduced graphene oxide (RGO) nanocomposites. In this study, TiO2-RGO nanocomposites were prepared by a facile and efficient one-step hydrothermal method using titanium (IV) butoxide (TBT) and graphene oxide (GO) without reducing agents. This method shows several unique features, including no requirement of harsh chemicals and high temperature involved, one-step hydrothermal reaction for mild reduction of GO and crystallization of TiO2 running in parallel, and the production of TiO2-RGO nanocomposites in a green and efficient synthetic route. In addition, the photocatalytic activities of the synthesized composites were systematically evaluated by degrading methylene blue (MB) under sun light irradiation. The TiO2-RGO nanocomposites show a superior photocatalytic activity to the synthesized pure TiO2. It is also found that the concentration of RGO in the nanocomposites plays a key role in the photocatalytic activity. Specifically, the composite with 1 wt % RGO shows the best photocatalytic activity, probably due to the reduction of the electron-hole recombination rate.

Patterning and reduction of graphene oxide using femtosecond-laser irradiation

Graphene has emerged as one of the most versatile materials ever discovered due to its extraordinary electronic, optical, thermal, and mechanical properties. However, device fabrication is a well-known challenge and requires novel fabrication methods to realize the complex integration of graphene-based devices. Here, we demonstrate direct laser writing of reduced graphene oxide using femtosecond-laser irradiation at λ = 795 nm. We perform a systematic study of the reduction process of graphene oxide to graphene by varying both the laser fluence and the pulse repetition rate. Our observations show that the reduction has both thermal and non-thermal features, and suggest that we can achieve better resolution and conductivity using kHz pulse trains than using MHz pulse trains or a continuous wave laser. Our reduced graphene oxide lines written at 10-kHz exhibit a 5 order-of-magnitude decrease in resistivity compared to a non-irradiated control sample. This study provides new insight into the reduction process of graphene oxide and opens doors to achieving a high degree of flexibility and control in the fabrication of graphene layers.

Statistical analysis of the reduction process of graphene oxide probed by Raman spectroscopy mapping

We propose a method for monitoring the large-scale homogeneity of the reduction process of graphene oxide. For this purpose, a Raman mapping technique is employed to probe the evolution of the phonon properties of two different graphene oxide (GO) thin films upon controllable thermal reduction. The reduction of GO is reflected by the upshift of the statistical distribution of the relative intensity ratio of the G and D peaks (ID/IG) of the Raman spectra and is consistent with the ratio obtained for chemically reduced GO. In addition, the shifts of the position distributions of the main Raman modes (, ) and their cross-correlation with the ID/IG ratio provides evidence of a change of the doping level, demonstrating the influence of reduction processes on GO films.

Molecular dynamic simulation of mechanical behaviour of RGO produced by thermal reduction method

Chemical oxidation of graphite and subsequent exfoliation allow the large-scale production of isolated graphene oxide (GO), in which the induced oxygen-containing functional groups on GO surface were then removed by means of reduction processes. The residual functional groups including carbonyl, hydroxyl and epoxy groups as well as the newly formed defects, significantly influence the physical properties of reduced GO (RGO). Here, RGO structures were generated through a thermal reduction process of GO using molecular dynamics simulations, in which the transformation of functional groups and the formation of non-hexagonal rings/defects were captured. The results suggested the formation of two RGO structures with different contents of functional groups at C/O ratios of about 11 and 13. These structures were obtained using various durations of the thermal reduction process. The dependence of tensile behaviour of RGOs on the structure and chirality as well as the influence of temperature on the tensile properties of RGOs were also evaluated. It was found that the strength and Young's modulus of RGOs decreased as a result of the residual functional groups and newly formed defects, and were decreased with the environment temperature.

Defect locating: One-step to monodispersed CoFe2O4/rGO nanoparticles for oxygen reduction and oxygen evolution

In this work, monodispersed CoFe2O4/reduced graphene oxide (rGO) nanoparticles have been successfully synthetized in one step from Co(Ⅱ) acetylacetonate, Fe(Ⅲ) acetylacetonate, benzylamine and graphene oxide (GO). A facile solvent method was designed to skillfully integrate the crystal growth process of CoFe2O4, the reduction process of GO and their compound process. In synthesis process, large numbers of defects on GO thin layers were smartly used to disperse CoFe2O4 nanoparticles. The micromorphology and the distribution of as-prepared samples were identified via X-ray diffraction (XRD), transmission electron microscope (TEM) and element mapping spectra. Results showed that the monodispersed CoFe2O4 nanoparticles were uniformly coupled with rGO thin layers. Good performance for both oxygen reduction and oxygen evolution of as-prepared CoFe2O4/rGO (0.92 V onset potential for oxygen reduction and 1.59 V overpotential at 10 mA cm−2 for oxygen evolution, vs. RHE) were found during a series of electrochemical tests, which make it a promising bi-functional catalyst in the field of fuel cells and metal-air batteries.

Facile in-situ design strategy to disperse TiO2 nanoparticles on graphene for the enhanced photocatalytic degradation of rhodamine 6G

Photogenerated electron/hole recombination greatly limits the catalytic efficiency of TiO2, and recently modification with graphene substance has been regarded as an effective way to enhance the photocatalytic performance of TiO2. When referring to the fabrication of graphene based materials, the reduction process of graphene oxide has been demonstrated to be a key step. Therefore, it is highly required to develop an efficient and simple route for the GO reduction and the formation of TiO2@rGO composites. In this study, we have demonstrated a facile and environmentally friendly strategy for in-situ preparation of the TiO2@rGO “dyade” hybrid and systematically investigated the photodegradation efficiency of the resultant composite by utilizing rhodamine 6G as the model pollutant. The obtained TiO2@rGO has a significant enhancement in photo energy adsorption leading to the effective photocatalytic degradation reactions. The results indicated that the best performance was conducted by the TiO2@rGO (10wt%, 120 min’s irradiation), which exhibited more than triple the higher photodegradation rate than commercial TiO2 (P25) nanoparticles mainly due to two aspects, the rapid separation of h+/e− and to improve adsorption. This work provides new insight into the synthesis of TiO2@rGO composites as a high performance photocatalyst for the degradation of organic contaminant.

How Oxygen‐Containing Groups on Graphene Influence the Antibacterial Behaviors

Graphene can be obtained with the reduction of graphene oxide (GO). Various reduction methods will result in different varieties and amounts of oxygen‐containing groups on the reduced graphene oxide (rGO) with diverse properties. In this work, rGO is fabricated on the titanium surfaces by the reduction process of GO through three types of reduction methods, for example, vacuum thermal annealing, hydrazine hydrate, and sodium borohydride chemical reduction. Results show that thermal annealing can remove carboxyl entirely at 600 °C for 1 h, and hydrazine hydrate can eliminate the oxygen functionalities, especially for epoxide. For sodium borohydride, it can dispose of carbonyl by converting carbonyl into hydroxyl. The rGO with different reduction process exhibits different responses for bacteria with higher numbers of carboxyl and hydroxyl/epoxide showing more effective antibacterial activities. It is concluded that carboxyl can inhibit the adhesion of bacteria on rGO surfaces by electrostatic repulsion and kill the bacteria with oxidative pressure mediated with the production of reactive oxygen species which is closely related with hydroxyl/epoxide. Furthermore, GO and rGO all exhibit excellent biocompatibility with no cytotoxicity.